Methodological studies for evaluation of groundwater flow system in a sedimentary rock area: Case study for the Boso Peninsula

Abstract

The regional groundwater flow system of the Yoro River basin, Boso Peninsula in Chiba Pref. in Japan was analyzed using data on river flow rates, and water chemistry and hydrogen/oxygen stable isotope ratios of rivers, springs, and wells. The relationship between the groundwater flow system and the geological structure was inferred from the hydrogeological analysis, and the origin of groundwater discharge and flow-paths from the geochemical approach.
The analysis indicated that a large part of the groundwater recharged at the highly permeable sand-dominant layer at high altitudes around the Daifuku Mt. flowing in the direction to strike of layers, and is discharged at the downstream basin as Ca-HCO₃(SO₄) type water. The rest of the Ca-HCO₃(SO₄) type water that recharged around the Daifuku Mt. is likely to flow into deep underground mixing with Na-HCO₃ type water, and be discharged at the downstream basin through fractures of low permeability alteration layer.